Microglia are resident immune cells of the CNS. They are involved in the pathogenesis of diverse neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, prion diseases as well as multiple sclerosis, amyotrophic lateral sclerosis and AIDS dementia complex. It is widely accepted that microglia contribute to the neurodegeneration through a release of a variety of proinflammatory substances. In fact, they are not the only cells which contribute to immunological processes inside the nervous system. The CNS is composed of different cell populations that answer to pathological factors and influence each other and modulate their reactions. These complex interactions are responsible for the development of brain pathology. This paper reviews the available information on microglial cells contribution to AD, PD and prion diseases development.